The present invention is directed to disk drives that employ a proximity recording interface in which the structure that supports the head contacts the disk during data transfer operations rather than flying above the disk during such operations. In particular, the present invention is directed to the cleaning of the structure that supports the head so as to prevent the head from becoming spaced from the disk to an extent that inhibits data transfer operations.
A disk drive is comprised of a magnetic disk that includes a plurality of concentric tracks for storing user data. A spin motor is employed in the drive to rotate the disk at a defined angular velocity so that data can be transferred between the disk and a magnetic/electrical transducer, which is typically referred to as a head. The head is a transducer that, when data is being written on the disk, converts an electrical signal representative of the data into a magnetic signal that is imprinted on the disk. Conversely, when data is being read from the disk, the head senses the magnetic signal representative of the data previously written on the disk and converts this magnetic signal into an electrical signal. Typically, the head is used to perform both read and write operations. However, certain disk drives employ separate heads for reading and writing data. The head is housed in a structure that is typically referred to as a slider. An actuator assembly serves to position the slider and head at specified locations over the disk. In the case of data transfers, the actuator assembly positions the head over a specified track on the disk. The actuator assembly is comprised of an actuator arm which has one end attached to the slider by a gimble-like connection and the other end attached to a motor that moves the arm to position the head at the desired location over the disk. Typically, the motor is a voice coil motor (VCM) that rotates the arm to radially position the head over a desired location on the disk.
For many years, the sliders and actuator arms of disk drives were designed to make use of the wind created by the spinning disk to fly the head above the disk and thereby avoid contact between the slider and the disk that could damage the disk and potentially result in the loss of data contained on the disk. The drawback of flying the head over the disk is that as the distance between the head and the disk increases, the amount of data that can be established on a given area of the disk decreases, i.e., the data density of the disk is reduced. Consequently, significant effort was expended in reducing the flying height of the head over the disk and thereby increasing the data density of the disk. However, as the flying height of the head was decreased, the ability to read and write data became increasingly affected by small particles on the disk surface. Specifically, when a low flying slider was contacted by one of the small particles on the disk, the particle, in many instances, caused the slider to jump away from the disk to a level at which read and/or write operations were adversely affected. Further, if there was enough energy in the collision, the resulting thermal effects would cause a crash that would destroy data and in some cases the head itself Consequently, various techniques were developed to remove debris from the disk to prevent such events from occurring.
Contrary to the popular belief that contact between the slider and the disk was to be avoided, a disk drive with a proximity recording interface was developed in which the slider contacts the disk during data transfer operations to position the head extremely close to the disk and thereby realize an increase in data density over disk drives that employ flying heads. With the slider in contact with the disk, cleaning of the disk is less of a concern because the slider tends to sweep particles out of the way as it moves over the disk surface during normal operations. However, due to the contact between the slider and the disk, the slider can accumulate debris that, as the debris accumulates, increases the spacing between the head and the disk. If the debris is allowed to accumulate unabated, the spacing between the head and the disk can reach a point at which data transfer operations are adversely affected. Moreover, because the debris is largely comprised of the lubricant forming the top layer of the disk, it can be thermally polymerized in certain situations to form a varnish-like material that is extremely difficult to remove and if of sufficient depth, can adversely affect the ability to do data transfer operations to an extent that the disk drive is essentially considered to be inoperable.
Based on the foregoing, there is a need for a disk drive with a proximity recording interface that is capable of cleaning the slider to avoid the accumulation of debris that could cause the head to be spaced a distance from the disk at which data transfer operations would be adversely affected and to prevent such debris from transforming into the noted varnish-like film that can render the drive virtually inoperable.
An object of the present invention is to provide a disk drive with a proximity recording interface that is capable of cleaning the slider portion of the interface to prevent debris from accumulating on the slider to a point at which the head is spaced from the disk at a distance that adversely affects data transfer operations.
It is a further object of the invention to provide a disk drive with a proximity recording interface that is capable of cleaning the slider portion of the interface to prevent the accumulation of debris on the slider that can form a varnish-like film that if allowed to accumulate can render the disk drive inoperable.
It is another object of the invention to provide a disk drive with a proximity recording interface that is capable of both cleaning the slider portion of the interface as well as redistributing the lubricant that forms the top layer of the disk, which has a tendency to migrate from the inner portion of the disk towards the outer portion of the disk due to the spinning of the disk.
It is yet another object of the invention to provide a disk drive with a proximity recording interface that both cleans the slider portion of the interface and also cleans debris residing of the surface of the disk that contributes to the accumulation of debris on the slider.
In one embodiment of the invention, a disk drive is provided that includes a spin motor for rotating a disk that can be either non-removable or removable by the user during normal operation of the disk drive, a head, a slider for housing the head, and an actuator assembly for moving the slider and head to desired positions over the disk. The slider includes a pad that houses the head and is defined by a leading edge, a trailing edge, and a curved or crowned surface that faces the disk and extends between the leading and trailing edges. Also included in the disk drive is a device for removing debris that may have accumulated on the pad during use of the disk drive.
In one embodiment, the noted device for removing debris causes the spin motor to rotate the disk at a lower angular velocity than during normal data transfer operations and further causes the actuator assembly to radially displace the slider and head. Low angular velocity spinning of the disk can be achieved using an open loop control for the spin drive motor. These operations cause the slider to rotate relative to the disk surface such that various portions of the curved surface of the pad are cleaned by the disk. Further, the disk is swept of debris to the extent of the radial displacement of the slider.
In a further embodiment, the noted device for removing debris causes the actuator assembly to displace the slider between the inner and outer radiuses of the disk, i.e., the range of radiuses on the disk over which the actuator assembly can position the slider. This serves to clean at least a portion of the pad and all of the disk over which the actuator assembly can position the slider. An open loop control can be used to achieve displacement of the slider, preferably after verifying that the disk is spinning.
In another embodiment, the noted device for removing debris causes the actuator assembly to radially displace the slider from an outer radial position to an inner radial position to clean at least a portion of the pad, sweep the disk over the area of radial displacement, and to redistribute the lubricant that has migrated towards the outer diameter of the disk due to the spinning of the disk.
In another embodiment, the device for removing debris causes the actuator assembly to radially displace the slider in both inward and outward radial directions relative to the disk. This serves to clean at least a portion of the pad, cleans the disk over the extent over which the slider is radially displaced, and to the extent the inward radial displacement and outward radial displacements overlap, evenly distributes the lubricant in this overlap region.
In yet a further embodiment of the invention, the device for removing debris is adapted to operate at times which the rotational velocity of the spin motor is increasing, such as when the disk drive is transitioning from a cold, start-up state to an operational state for data transfers, and when the disk drive is transitioning from an energy saving state in which the rotational velocity of the spin motor has been reduced to save power to a state at which the rotational velocity of the spin motor has increased, such as the noted operational state.
In a further embodiment, the device for removing debris is adapted to operate at times when the rotational velocity of the spin motor is decreasing, such as going from an operational state to a cold, start-up state or an energy saving state.
A further embodiment of the invention employs a device for removing debris that is adapted to operate at times when the pad is expected to have accumulated debris. For instance these times can be periodic during, for example, extended operation of the disk drive. In another situation, these times can be based upon the prior use of the disk drive apparatus. For example, the previously noted varnish-like film is believed to form when the pad is positioned over one or several closely positioned tracks for an extended period of time such that heat is produced which polymerizes any lubricant on the pad into the varnish-like film. In such a situation, the device for removing debris can be adapted to sense this situation and then operate at times or intervals to prevent the formation of the varnish-like film.
Another embodiment of the invention employs a device for removing debris that operates as part of an error recovery operation. More specifically, during a read or write operation, an error in transferring the data between the disk and the head may be detected. As part of an operation to correct the error, the device for removing debris is used to remove debris from the proximity recording interface before the failed data transfer operation is retried.